Capacitive touch sensing is used on many products for controls and other applications. Capacitive sensors can be used to detect position or proximity, and are often used in two-dimensional touchpads, touch displays, slide controls, and other types of input interfaces. These input interfaces are commonly utilized by mobile phones, computers, personal digital assistants, and other electronic devices. A device user operates such an electronic device by moving one or more fingers in proximity to or in contact with a sensing region of one or more capacitive sensors at the input interface. One advantage of the use of capacitive touch sensing in electronic devices is that sensing can occur below the device plastic housing without any top level alterations.
Capacitive touch sensors operate by monitoring the change in capacitance above a parasitic capacitance background when a conductor such as the user finger comes in close proximity to or in contact with a sense electrode. Capacitive touch sensing requires each electrode to be physically and electrically separate from the ground of the system and any other nearby conductors or sensor electrodes in order to measure capacitive changes for that particular electrode. Electrically separate in particular means that capacitive coupling is low as this reduces the system sensitivity.
Often a surface finish is put on the plastic for cosmetic purposes. In particular, metallization is sometimes used to give the product a particular look. A conductive material deposited on the device surface may also be used to highlight the location of an underlying sensor or aid in sensing by the underlying sensor. Regardless of the purpose of the conductive material, placing conductive materials over a capacitive touch sensitive area may violate the conductive separation between each underlying sensor “pad” area. Although the surface conductive material is physically separate from the underlying electrodes, it may capacitively couple them together if improperly placed on the device surface. As a result, improved apparatuses and methods for capacitive sensing are needed.